232. Implement Queue using Stacks
阿新 • • 發佈：2017-10-24
ole and push emp mean void ati whether style
Implement the following operations of a queue using stacks.
- push(x) -- Push element x to the back of queue.
- pop() -- Removes the element from in front of queue.
- peek() -- Get the front element.
- empty() -- Return whether the queue is empty.
Notes:
- You must use only standard operations of a stack -- which means only
push to top,peek/pop from top,size, andis emptyoperations are valid. - Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
- You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
題目含義：使用stack來實現queue的功能
1 class MyQueue { 2 Stack<Integer> input = new Stack(); 3 Stack<Integer> output = new Stack(); 4 /** Initialize your data structure here. */ 5 public MyQueue() { 6 7 } 8 9 /** Push element x to the back of queue. */ 10public void push(int x) { 11 input.push(x); 12 } 13 14 /** Removes the element from in front of queue and returns that element. */ 15 public int pop() { 16 peek(); 17 return output.pop(); 18 } 19 20 /** Get the front element. */ 21 public int peek() { 22 if (output.empty()) 23 while (!input.empty()) 24 output.push(input.pop()); 25 return output.peek(); 26 27 } 28 29 /** Returns whether the queue is empty. */ 30 public boolean empty() { 31 return input.empty() && output.empty(); 32 } 33 }
232. Implement Queue using Stacks